This invention relates to hydraulic ram safety apparatus, and more particularly to an improved hydraulic elevator safety brake having wedge-shaped braking members which are released in the event of a failure condition to wedge against and stop downward movement of the elevator's piston.
Hydraulic elevator safety devices of the type to which this invention relates are shown generally in U.S. Pat. Nos. 3,783,976, 3,783,983 and 3,995,534. All of these patents show hydraulic elevator safety brake systems having wedge-shaped braking members actuated to be released downwardly to wedge against the elevator's piston in response to a failure condition in the elevator.
U.S. Pat. No. 3,783,976 shows such braking members actuated in response to a drop in system pressure. U.S. Pat. No. 3,783,983 shows a device which functions somewhat similarly, but also including actuation of its wedge-shaped braking members in response to an overspeed condition of the elevator. U.S. Pat. No. 3,995,534 disclosed a brake system of the same general type, but wherein each of a series of wedge-shaped braking members around the piston was controlled directly by its own piston and cylinder positioned below the braking member. This differed from the other two patents, which utilized a lever connected to all the braking members and held in an disengaging position so long as no failure condition occurred, i.e. loss of system pressure or overspeeding. The lever was connected to an actuating hydraulic cylinder in communication with elevator system pressure, for holding the lever toward the disengaged position until a pressure drop occurred to permit the lever to move to the position of brake engagement.
The wedge-shaped braking members in each of these prior art systems were cylindrical at the inner face, for engagement against the elevator's piston, but the outer surfaces, which were positioned to slide along complementary surfaces in the supporting housing, were planar. In U.S. Pat. No. 3,783,976, for example, the two opposed braking members which appeared rectangular in plan view except for the half-circular cutout in each braking member for engaging the piston. In U.S. Pat. No. 3,995,534, three braking members were provided, forming generally the shape of a truncated cone at their exterior surfaces, and the surrounding housing was also circular, but the actual mating surfaces of the brake sections and the housing for travel of the brake sections down into the engaged position were planar. In fact, roller bearings were shown between the brake sections and the housing in that patent.
This latter construction required additional machining operations and a multiplicity of components and manufacturering steps, and would not be as economical to produce as the invention described below. In addition, three relatively small planar areas of the generally circular housing were expected to carry the very high wedging forces exerted outwardly when the full weight of the elevator car and piston was impacted to the braking members, pushing them downwardly. Unless the housing were of very great bulk and strength, this would tend to distort its shape.
None of the prior art elevator safety brake systems was as simple and economical to produce, while of very high strength to weight ratio, as is the present invention described below.